1. Field of the Invention
The present invention relates to a method of manufacturing a substrate provided with a semiconductor layer with an insulating layer therebetween, and particularly relates to a method of manufacturing an SOI (silicon on insulator) substrate. The present invention also relates to a method of recycling a semiconductor substrate in the method of manufacturing a substrate provided with a semiconductor layer with an insulating layer therebetween.
2. Description of the Related Art
As a substrate suitable for manufacturing a low power consumption semiconductor device capable of high-speed operation, an SOI substrate in which a semiconductor layer is provided over a base substrate having an insulating surface is receiving attention.
One of known methods of manufacturing an SOI substrate is a hydrogen ion implantation separation method (see Patent Document 1). The hydrogen ion implantation separation method is a technique in which an oxide film is formed on a silicon wafer and serves as a bonding film, and a microbubble layer is formed in the silicon wafer by implanting hydrogen ions or noble gas ions into the silicon wafer from the upper surface thereof. An oxide film may be formed as well on a silicon wafer which is to be used as a base substrate. Then, the surface of the silicon wafer into which ions are implanted is put in close contact with the other silicon wafer, which serves as a base substrate, with the oxide film therebetween. By the heat treatment performed afterwards, a thin layer is separated from the former silicon wafer with the microbubble layer used as a cleavage plane. Further heat treatment strongly bonds the silicon wafers so that an SOI substrate is formed.
Research has been conducted on a method of manufacturing a plurality of SOI substrates using as small a number of silicon wafers as possible so that silicon wafers are used effectively and economically (see Patent Document 2).
Since the shape of the split silicon wafer is preserved, the silicon wafer can be reused in order to manufacture another SOI substrate after that a remaining layer over the separation plane is removed by etching or polishing.
As described above, in the case of using a silicon wafer repeatedly, the thickness thereof is reduced. Thus, a method has been proposed in which a silicon wafer which cannot stand a process of manufacturing an SOI substrate is utilized in other uses.
[Citation List]
    [Patent Document 1] Japanese Published Patent Application No. 2000-124092    [Patent Document 2] Japanese Published Patent Application No. 2000-349266
However, a method in which a thinned semiconductor substrate is used in a process other than manufacture of SOI has problems. There are a limited number of uses or processes to which thin semiconductor substrates can be applied, which causes limitation on uses or processes in which it is used. Due to this limitation, the efficiency of another process in which the thinned semiconductor substrate is used is likely to be lowered. In addition, in a process of manufacturing an SOI substrate, it is difficult to substantially improve the use efficiency of a thinned semiconductor substrate in consideration of another use or process in which the thinned semiconductor substrate is used. Still, in manufacturing an SOI substrate, a semiconductor substrate is expensive; therefore, it is important to reduce cost by improving the use efficiency of a semiconductor substrate.